Heat activated curing system for organosilicon compounds



vulcanized, or cured configuration.

United States Patent 3,192,181 HEAT ACTIVATED CURING SYSTEM FQRORGANOSILICON COMPOUNDS Ronald F. Moore, Midland, Mich., assignor to DowCorning Corporation, Midland, Mich., a corporation of Michigan NoDrawing. Filed June 18, 1962, Ser. No. 202,974 25 Claims. (Cl. 260-465)Thisinvention relates to a new heat activated curing system fororganosilicon compounds.

Many articles of commerce based on organosilicon compounds are of thetype that can be easily formed to a desired shape or applied to adesired area, after which the easily worked material is then cured toretain its desired configuration. For example, polysiloxane elastomersare normally supplied as formable materials rang ing from thin pastes tostifi plastic dough-like materials. These materials are shaped by suchas molding and extruding, after which the article is converted to therubbery state by curing, aprocess often called vulcanization whenapplied to an elastomer. The article then retains its desired shape, orif deformed, will seek to return to its Similarly, polysiloxane resins,obtainable as fluids, fusible solids .and solutions are also formed orapplied and thereafter cured.

The curing methods employed for organosilicon compounds can be placedinto two classes. The first are those that occur spontaneously at roomtemperature, exemplified by the curing systems such as described in U.S.Patents 2,833,742, 2,843,555, 2,902,467, 2,934,519 and 2,999,077. Thesecond are those that require beat to :activate .the curing reaction,such as organic peroxides, and the various sulfur-type cures morecommonly used in connection with organic rubber. The instant compositionis of the latter type, that is, it is heat activated. The system issimilar to the curing system described in U.S. Patent 3,020,260, butdiliers therefrom in that the instant system is inactive at roomtemperature.

It is an object of the present invention to provide a novel useful heatactivated curing system for organosilicon compounds.

Another object is to provide a curing system that can be incorporatedinto an organosilicon compound that is inert at normal temperatures.

A further object is to provide a curing system that is not inhibited byair or components of air.

A further object is to provide a heat activated cure for organosiliconcompounds that imparts good stability to becured system.

These and other objects will be apparent iro-m the followingdescription.

' This invention discloses a new organosilicon composition comprising(1) an organosilicon compound having an average of from one to threegroups per silicon atom selected from the group consisting of monovalenthydrocarbon radicals, aliphatic-nusaturation-free monovalenthalo'hydrocarbon radicals, and cyanoalkyl radicals, there being anaverage per molecule of (1) of at least two monovalent hydrocarbonradicals containing aliphatic unsaturation, the remaining valences ofthe silicon atoms of the said organosilicon compound being satisfied byselection from the group consisting of divalent ogygen Iatoms, divalenthydrocarbon radicals, divalent hydrocarbon ether radicals and divalenthaloa-rylene radicals, (2) Ian organosilicon compound containingsilicon-bonded hydrogen atoms, there being in addition an average of upto two radicals per silicon atom selected from the group consisiting ofmonovalent hydrocarbon radicals free of aliphatic unsaturation,monovalent halohydrocarbon radicals free of aliphatic unsaturation andcyanoalkyl radicals, .the remaining valences of the silicon atoms beingsatis- I 3,192,181 Patented June 29, 1965 "ice fied by radicals selectedfrom the group consisting of divalent oxygen atoms, divalent hydrocarbonradicals free of aliphatic unsaturation, divalent hydrocarbon etherradicals free of aliphatic unsaturation and divalent baloaryleneradicals, there being an average of at least two silicon-bond-edbydrogen atoms per molecule of (2), the sum of the average number ofaliphatic unsaturated monovalent radicals per molecule of (l) and theaverage number of silicon-bonded'hydrogen atoms per molecule of (2) isgreater than '4, (3) a platinum catalyst in an amount of at least 0.1part per million Pt based on the combined weights of 1) and (2), and (4)at least one part :per part of -(3) of benz-ot-riazole.

Oranosilicon compound 1) can be a resin, a fluid or a substantiallynon-flowing 'high polymer such as conventionally used in silicone rubbermanufacture. Any monovalent hydrocarbon radical, halohydrocarbon radicalor cyanoalkyl radical that can be used with organosilicon compounds asstated above is operable in component (1). Examples of monovalenthydrocarbon radicals that can be used include, -for example, alkylradicals such as methyl, ethyl, isopropyl, tert butyl, octadecyl andmyricyl; cycloalkyl radicals such as cyclopentyl and cyclohexyl; aralkylradicals such as benzyl and 2-phenylethylg aryl radicals such as pbenyl,tolyl, xyly-l, naphthyl, xenyl and anthr-acyl; and radicals containingaliphatic unsaturation such as vinyl, allyl, methallyl, ethynyl,butadienyl, cyclopentenyl, rn-vinylphenyl and the like.

Any monovalent halohydrocarbon radical and cyanolalkyl radical can beused in (1), and include, for example, chloromethyl,3,3,3-trifiuoropropyl, 2,3-dibromocyclopentyl, iodophenyl,dichloronaphthyl, Qcyanoet'hyl, 2-cyanopr-opyl, andomega-cyanooctadecyl.

in component (1) there must be an average per molecule of at least tworadicals containing aliphatic unsaturation. These radicals enter intothe curing reaction discussed below. More than two said radicals can bepres ent, but a minimum of two (average per molecule) is necessary toobtain a cure to a coherent solid. When the average number ofaliphatically unsaturated radicals per molecule is more than two, acorrespondingly tighter cure is obtained.

The monovalent organic radicals in (1) can be the same or different. Inaddition, the aliphatically unsaturated radicals can be the same ordififerent. As well, organosilicon compound (1) can be a copolymer ormixture of copolymers.

The remaining valences of the silicon atoms in organosilicon compound(1) are satisfied by divalent oxygen, divalent hydrocarbon radicals,divalent hydrocarbon ether radicals and divalent haloarylene radicals.Any one or more of the said divalent linkages can be present incomponent (1).

Examples of divalent radicals that can be used in component (1) include,for example, hydrocarbon radicals such as ,and-

hydrocarbon ether radicals such as CH OH OOH OHz-, cmornomoomomandhaloarylene radicals such as F F 01 I I Br Br Any of the divalentlinkages stated above can be present in component (1). However, wherethe average number of silicon atoms per molecule is greater than three,it is preferred when use of the finished product will include bothextremely high and extremely low temperature exposure, that at least 50percent of the divalent linkages be oxygen. This is not necessary,however, particularly whencomponent (1) is a cyclic material.

Preparation of materials that can be component (1) are Well known in theart. The monovalent radicals can be attached for instance, by either theso-called direct process, or via Grignard reactions, or in some cases bya pseudo Friedel-Crafts reaction. Other reactions normally used tointroduce organic radicals can of course be also used. Silicon-bondedoxygen is introduced by hydrolysis of a hydrolyzable group on silicon(such as halogen, alcoholoxy or acyloxy) as well known in the art.Divalent organic radicals can be introduced via Wurtz-type synthesis,Grignard, direct process, etc.

and

The preparations of compounds suitable for use as com-- ponent (1) arewell known in the art and need not be recited herein.

Organosilicon compound (2) can be any compound as above defined. It cancontain two or more silicon-bonded hydrogen radicals per molecule and inaddition an average of up to two monovalent radicals per silicon atom asabove set forth. These can include, for example, alkyl radicals such asmethyl, ethyl, isopropyl, tert-amyl, octadecyl and myricyl; cycloalkylradicals such as cyclopentyl and cyclohexyl; aralkyl radicals such asbenzyl, fl-phenylethyl and xylyl; and aryl radicals such as phenyl,tolyl, xenyl, naphthyl and anthracyl. In addition, monovalenthalohydrocarbon radicals such as chloromethyl, 3,3,3-trifluoropropyl,a,a,a-trifiuorotolyl, bromophenyl and 2,3-dibromocyelopentyl can bepresent in component (2). Also, cyanoalkyl radicals such as cyanoethyland cyanobutyl can also be present. The organic radicals' can be alikeor diiferent. Component (2) can, in addition, be a copolymer or mixtureof two or more copolymers, provided only that the copolymers are free ofaliphatic unsaturation and each contain an average per molecule of atleast two silicon-bonded hydrogen atoms.

The remaining valences of the silicon atoms of component (2) aresatisfied from divalent oxygen, divalent hydrocarbon radicals free ofaliphatic unsaturation (e.g.

' important.

etcf), divalent hydrocarbon ether radicals free of aliphaticunsaturation (e.g.

etc), and divalent haloarylene radicals (e.g.

etc.). Any one or more of the above said divalent linkages can bepresent in component (2). As with component (1), when the average numberof silicon atoms per molecule of (2) is greater than three it ispreferred that at least 50 percentof the above divalent linkages beoxygen. This is not necessary, however, especially when component (2) isa cyclic material.

Preparation of materials that come within the definition of component(2) are well known in the art, and many examples of such materials areavailable commercially. Thus, recitation of methods of manufacture ofthese materials would be redundant herein.

The selection of components (1) and (2) is somewhat inter-related. Whenthe. average number of aliphatically unsaturated groups per molecule incomponent (1) is 2.0, a component (2) should be selected wherein the.average number of silicon-bonded hydrogen atoms per molecule is greaterthan 2.0, so that the total of these just defined quantities is greaterthan 4. The analogous is true when the chosen component (2) contains 2.0(average) silicon-bonded hydrogen atoms per molecule. When eithercomponent has the defined quantity greater than 2.0, selection of theother component on this basis is irrelevant. It should be understood ofcourse, that the higher the sum of these quantities, the more highlycrosslinked can be the cured composition.

The molar ratio of aliphatic unsaturated radicals in (1) to thesilicon-bonded hydrogen atoms in (2) can in some cases be an importantconsideration. Where it is important, the ratio of these two should bepreferably between 0.67 and 1.5. However, there are many instanceswherein a balance'of these two quantities is un- For example, if acomponent (1) has, say, an average of six aliphatic unsaturated groupsper molecule, the use of equal molar amounts of silicon-bonded hydrogenatoms may well. give a cure too tight for the desired end use. Thus,less than, sometimes much less than, .the equal molar amount of SiHwould be used to provide the desired degree of cure. However, whenmaximum stability is required it is desirable to match the molarquantities of silicon-bonded hydrogen atoms in (2) to the aliphaticunsaturated radicals in (1).

Platinum compound (3) can beany of the known forms, ranging fromplatinum as such or as deposited on carriers such as silica gel orpowdered charcoal, to platinic chloride, salts of platinum andchloroplatinic acid. Any of these forms will function in the instantcuring system. A preferred form of platinum is the chloro platinic acideither as the commonly obtainable. hexahydrate or the anhydrous form, onaccount of its easy dispersability in organosilicon systems and itsnon-effect on color of the mixture.

There should be at least 0.1 part per million of plati:

num present in the mixture, based on the combined total weight of (1)and (2). However, since impurities in the system can easily poison thissmall quantity of catalyst, it ispreferred to employ from 1 to 20 partsper million of platinum. A greater amount of the platinum does notaffect the reaction, but does affect the requirement of component (4)below, and economic considerations suggest the lower amounts mentioned.

The key component of the instant composition is benzotriazole. Whenpresent in sufficient amount, this component completely prevents theplatinum from catalyzing at room temperature (and up to about 60 C.) thereaction between the SiH in (2) and aliphatically unsaturated radicalsin (1). The amount of benzotriazole required depends on (a) the amountof platinum, (b) the form of platinum catalyst, and (c) the precence orabsence of some non-essential components. There must be present at leastone part of benzotriazole per part of platinum. When, for instance,chloroplatinic acid is used, the requirement of benzotriazole may benearer two parts per part of platinum. When, for example, silica fillersare present, the benzotriazole requirement may increase to 5 to 50 partsper part of platinum, dependent on the type of silica. Dispersions ofcompounds in organic solvents such as xylene can some time effect thebenzotriazole requirement. The benzotriazole requirement has varied infiller-containing organosilicon rubber compositions all the way fromabout 1 0 to nearly 200 parts per part of platinum.

Regardless, for any overall matrix involving this curing system, thereis an easily determined minimum requirement of benzotriazole that willeffectively neutralize at, ordinary temperatures the catalytic tendencyof the platinum toward causing interaction of SiH groups withaliphatically unsaturated radicals, which requirement ranges up to morethan 200 parts of benzotriazole per part of platinum, depending asalready stated on the matrix in which it is employed. This minimum iseasily determined by the skilled worker. There is no advantage, neitheris there disadvantage other than waste of benzotriazole to use more thanthe minimum amount, although it may be preferred to use about 50 percentexcess of benzotriazole over the minimum determined amount as a safetymargin. Even at these levels, the amount of benzotriazole normally addedis measured in only up to hundreds of parts per mililon, or quite a bitless than 0.1 percent of the combined weights of components (l) and (2).The use of benzotriazole to completely prevent room temperature cure ofthe stated organosilicon system is only one way in which'it can beemployed. Benzotriazole can also be added in less than sufiicient amountthat completely prevents curing at room temperature. In this event therate of cure at room temperature of the system is slowed according tothe amount of benzotriazole added. This is extremely useful in a systemwhich, if comprising only components (1), (2) and (3) of this inventionwould cure in, say, four hours at room temperature, but which with theaddition of the proper amount of benzotriazole would require, forinstance, 24 hours at room tempera ture. This would allow an end-user amuch longer time in which to use the mixture for coating, dipping,spraying, etc., before any given mixture became cured. In this use ofbenzotriazole its inhibiting effect can be negated by heating thecomposition, preferably above 70 C., to hasten the cure.

Thus, the key component of this invention, which is benzotriazole, canbe used to retard the room temperature cure or prevent the roomtemperature cure (infinite retardation) of a system which cures by theplatinumcatalyzed interaction of SiH with unsaturated aliphatic radicalson silicon.

As in the case wherein suflicient benzotriazole is used to prevent roomtemperature cure, the amount of benzotriazole used to retard the saidcure is dependent upon the amount and nature of the platinum catalystand other components in the system to be cured. In addition, morebenzotriazole will give more retardation, while less will give lessretardation. The amount of benzotriazole to be used in a given system toobtain a given retardation is easily determined by the skilled worker.

The components of this invention can be mixed in any order. While theaddition of the platinum without the benzotriazole will cause thebeginning of interaction of components (1) and (2), the extent ofreaction in a few minutes time at ordinary temperatures is negligible,within which time the benzotriazole will normally have been added. Insystems where even this small amount of interaction might bedeleterious, the benzotriazole can be added before the platinum. Apreferred method of mixing is to premix components (1) and (3), premixcomponents (2) and (4), and then combine these two premixtures. Anotherpreferred method is to add the benzotriazole to component (1) and thenadd the remaining components. However, a set order is not necessary tothe functioning of this curing system.

The system can be mixed just prior to use (contemplated cure) or can bemixed and stored for later use. In addition, one or more of thecomponents can be omitted, provided only that when components (1), (2)and (3) are present, component (4) must also be present. In addition,the storage of a mixture of components (2) and (3) alone is notpreferred, for should moisture be present or be introduced, .anundesirable alternate reaction can occur. Thus, components (1), (2) and(4) can be stored together and component (3) added later, or (1), (3)and (4) to which (2) is added later, etc. Further, components (2), (3)and (4) can be conveniently stored together and added to component (1)when desired. Such a system is especially desirable in the siliconerubber field, wherein the diorganopolysiloxane polymers each haveessentially the same amount of aliphatic unsatu-ration, wherefore theaddition of components (2), (3) and (4) as a premixture is quitefeasible.

As stated earlier, with suificient benzotriazole the curing system isstable; that is, it does not cause curing of the organosiliconcomposition, at ordinary temperatures. For instance, even at 49 C. F.) afluid composition corresponding to the instant invention with suflicentbenzotriazole showed essentially no change in viscosity after 4 days. At70 C., however, this same mixture was a vulcanized rubber after 24hours, and at C. it vulcanized within 10 minutes. Thus, the instantcuring system is quite stable to about 50 to 60 C., well above ordinarytemperatures.

The curing reaction is that of addition of an SiH of (2) to anunsaturated radical on silicon of (1). This is a well known reaction,catalyzed by many other materials in addition to platinum. The additionof SiH to allyl on silicon serves to illustrate the reaction as follows:

ESiH OH =CHCH SiE ESlCHzCHzCH SlE system. It is also well recognizedthat neither the extent of cure nor rate of cure are inhibited by air orcomponents thereof.

In addition to the recited components, other materials can be present ina composition utilizing this cu ring catalyst system. Such materials asare ordinarily used in organosilicon compositions, such as fillers(carbon black, silica 'aerogels, silica soots, treated silicas, alumina,clays, metal oxides, metal carbonates, metal silicates, etc.),

pigments to impart certain colors to the material, rubber additives suchas compression set aids, plasticizers (both organosilicon and organic),etc., can be added to the instant composition. Materials that are knownto poison platinum catalysts should of course be excluded, but these arenot normally included in organosilicon compounds designed to be cured byheat activated curting catalysts.

The instant composition can be used for any application requiring aresin or rubber where heat activated curing is possible. One willimmediately recognize the tremendously wide variety of applicationsherein included.

The instant curing system can be activated in closed or open systems, in.thin or thick sections and under pressure and at atmospheric pressurewith equal ease merely bythe application of heat above about 70 C.,there being complete freedom from the undesirable sponging associated.with some curing systems when pressure is not used, and freedom fromuncured surface, obtained particularly with organic peroxides, when thecomposition is cured in the open exposed to the atmosphere. Thus,advantages of this particular system include excellent thick-sectioncure, absence of air-inhibition, and therefore uniform cure throughoutthe sample. In addition, where desired, the system can serve to control(slow down) .the rate of cure of a platinum catalyzed SiH- unsaturatedaliphatic-on-s'ilicon room temperature cure.

The following examples are illustrative only and should not be construedas limiting the invention which is properly delineated in the appendedclaims. All parts are by weight.

EXAMPLE 1 Two siloxane mixtures were prepared of the followingcomposition. Sil-oxane A:

100 parts of a dimethylvinylsiloxy-endblocked dimethylpolysiloxanehaving a viscosity of 2,500 cs. at 25 30 parts of calcined diatomaceousearth,

25 parts of fine particle size zirconium silicate,

1 part of butylcarbitol acetate containing 0.19 percent platinum aschloroplatinic acid.

Siloxane B:

100 parts of the same dimethylpolysiloxane as in A,

120 parts of calcined diatomace-ous earth,

25 parts of fine particle size zirconium silicate,

40 parts of a mixture of iron oxide in a hydroxylated low viscositydimethylpolysiloxane, there being 7 percent by weight of iron in themixture,

59.5 parts of a trimethylsiloxy-endblocked methylhydrogenpolysiloxanehaving an average per mole cule of 10 silicon atoms.

For sample C below, 100 parts of siloxane A and 4 parts of siloxane Bwere mixed and the tests conducted as shown in Table I.

For sample D below, 100 parts of siloxane A, 4 parts of siloxane B and0.06 part of a paste containing 50 percent by weight of benzotriazoleand 50 percent by weight of a trimethylsiloxy-endblockeddimethylpolysiloxane having a viscosity of 100 cs. at 25 C. weremixed,-and the tests conducted as shown in Table I. This compositioncontains 11 parts per million platinum and 290 parts per millionbenzotriazole.

Norn.These samples vulcanized to rubber when heated 15 minutes at 150 C.

8 EXAMPLE 2 Siloxane mixture E was prepared of the followingcomposition:

100 parts of a vinyldimethylsiloxy-endblocked dimethylpolysiloxanehaving a viscosity of 2,500 cs. at 25 C. parts of ground quartz havingan average particle size of 5 microns, I 1 part of butylCarbitol-acetate containing 0.19 percent platinum as chloroplatinicacid.

Table II Time after mixing Sample Ratio to 0 viscosity Viscosity 12,000as 53,000 cs 4. 4 168,000 vs 14. 0 Rubber 15,000 cs 40,000 cs-.. 142,000cs Rubber EXAMPLE 3 Equivalent results are obtained when powderedplatinum metal or platinum supported on gamma-alumina are substituted inequivalent amount for the butylv Carbitol acetate solution ofchloroplatinic acid in Example 1.

EXAMPLE 4 Table 111 Sample Time after Viscosity, cs. Useful life ofmixing fluid 0 22,000 I 1 hr (Gelled) 20 minutes.

24 hrs (Rubber) 0 2 weeks.

2 weeks 12, 500

Useful life of fluid is the time fluid can be used for applicationbefore it becomes too thick and/or gelled.

EXAMPLE 4 When any of the following polysiloxanes are substituted forthe dimethylpolysiloxane in siloxane A and the mixtures made per sampleD as in Example 1, mix tures which are more stable (that is, do notvulcanize asreadily) at room temperature are formed.

(a) A methylphenylallylsiloxy-endblocked methyl-3,3,3-

fiuoropropylpolysiloxane having a viscosity of 50,000 cs. at 25 C.

(b) A -dimethylcyclopentenylsiloxy endblocked copolymer containing about50 mol percent ethylmethyl- 9 siloxane units, 5 mol percent'octadecylmethylsiloxane units, 20 mol percent2-phenylethylmethylsiloxane units and 25 mol percent units of theformula and having a viscosity of 250,000 cs. at 25 C.

(c) A mixture of (1) 10 parts of a Z-butynyldimethylsiloxy endblockedfi-cyanoethylmethylsiloxane fluid having a viscosity of 700 cs. at 25 C.and (2) 90 parts of a hydroxy endblocked copolymer containing 98 molpercent chlorophenylmethylsiloxane units and 2 mol percentvinylethylsiloxane units, having a viscosity of 550 cs. at 25 C.

'(d) A vinyldimethylsiloxy-endblocked copolymer containing 50 molpercent dimethylsiloxane units, 10 mol percent diphenylsiloxane units, 5mol percent benzylmethylsiloxane units and 35 mol percent units of theformula and having a viscosity of 25,000,000 cs. at 25 C.

(c) A copolymer containing 89.86 mol percent dimethylsiloxane units,0.14 mol percent methylvinylsiloxane units and 10 mol percent units ofthe structure --(CH SiCH Si(CH having a Williams plasticity of 0.100inch.

EXAMPLE When equivalent quantities of the following org-anosiliconcompounds are substituted for the methylhydrogenpolysiloxane of siloxaneB and the resulting mixture used as in sample D of Example 1, similarresults are obtained:

e 5 HSi OSi OSiH I 1181 OSi OSiH (EH, ta tea as] a s 10 parts of w OSiHHSi l and 5 parts of ([3113 l (H13 Hs PQs iH CH3 CH3 EXAMPLE 6 Whensufficient benzotriazole is added to the following mixture, theresulting composition is stable at ordinary temperatures, but can becured to a coherent solid by heating at a temperature above 70 C. untilthe desired cure is obtained:

parts of a phenylmethylhydrogensiloxy-endblocked dimethylpolysiloxanehaving a viscosity of 100,000 cs. at 25 C.,

2.0 parts of fluid copolymer of the average composition 0.0002 part ofplatinum added as a solution of platinum sulfate in ethanol.

That which is claimed is:

1. A composition of matter comprising (1) an organosilicon polymerhaving an average of from one to three groups per silicon atom selectedfrom the group consisting of monovalent hydrocarbon radicals,aliphatic-unsaturation-free monova-lent halohydrocarbon radicals, andcyanoalkyl radicals, there being an ave-rage per molecule of ('1) of atleast two monovalent hydrocarbon radicals con-taining aliphaticunsaturat-ion, the remaining valences of the silicon atoms of'the saidorg-anosilicon polymer being satisfied by selection from the groupconsisting of divalent oxygen atoms, divalent hydrocarbon radicals,divalent hydrocarbon ether radicals and divalent haloarylene radicals,said divalent radicals linking silicon atoms,

(2) an organosilicon compound containing siliconbonded hydrogen atoms,there being in addition an average of up to two groups per silicon atomselected from the group consisting of monovalent hydrocarbon radicalsfree of aliphatic unsaturati-on, monovalent halohydrocarbon radicalsfree of aliphatic un saturation and cyano-alkyl radicals, the remainingvalences of the silicon atoms being satisfied by groups selected fromthe group consisting of divalent oxygen atoms, divalent hydrocarbonradicals free of aliphatic unsaturation, divalent hydrocarbon etherradica-ls free of aliphatic unsaturation and divalent haloaryleneradicals, said divalent radicals linking silicon atoms, there being anaverage of at least two siliconbonded hydrogen atoms per molecule of(2), the sum of the average number of aliphatic unsaturated monovalentradicals per molecule of (1) and the average number of silicon-bondedhydrogen atoms per molecule of (2) being greater than 4,

(3) a platinum catalyst in an amount of at least 0.1 part per million Ptbased on the combined weights of (1) and (2), and

(4) at least one part by weight per part of (3) of benzotriazole.

2. A composition of matter comprising (1) a triorganosilyl endblockeddiorganopolysiloxane having a viscosity of at least 100 cs. at 25 C.wherein the organic radicals are selected from the group consisting ofmonovalent hydrocarbon radicals, aliphatic-unsaturation-free monovalenthalohydrocarbon radicals, and cyanoalkyl radicals, there being anaverage per molecule of (1) of at least two monovalent hydrocarbonradicals containing aliphatic unsaturation and in which up to 50 percentof the silicon atoms in the said siloxane can be connected by organicradicals selected from the group consisting of divalent hydrocarbonradicals, divalent hydrocarbon ether radicals, and divalent haloaryleneradicals,

(2) anorganosilicon compound containing siliconbonded hydrogen atom-s,there being in addition :an average of up to two groups per silicon atomselected from the group consisting of monovalent hydrocarbon radical-sfree of aliphatic unsaturation, monovalent halohydrocarbon radicals freeof aliphatic unsaturation and cyanoalkyl radicals, the remainingvalences of the silicon atoms being satisfied by groups selected fromthe group consisting of divalent oxygen atoms, divalent hydrocarbonradicals free of aliphatic unsaturation, divalent hydrocarbon etherradicals free ofaliphatic unsaturation and divalent haloaryleneradicals, said divalent-radicals linking silicon atoms,

there being an average at least two silicon-bonded hydrogen atoms permolecule of (2), the sum of the average number of aliphatic unsaturatedmonovalent radicals per molecule of (1) and the average number ofsilicon-bonded hydrogen atoms per molecule of (2) being greater than 4,

(3) a platinum catalyst in an amount of at least 0.1 .part per millionPt based on the combined weights of (l) and (2), and

(4) :at least one part by weight per part of (3) of homotriazole.

3. A composition of matter according to claim 2 wherein the organicradicals of (1) are methyl and vinyl.

4. A composition of matter according to claim 2 wherein the organicradicals of (1) are methyl, phenyl and vinyl.

5. A composition of matter according to claim 2 wherein the organicradicals of (1) are methyl, 3,3;3-trifluoropropyl and vinyl.

6. A heat curable composition of matter comprising (1) an org-anosiliconpolymer having an average of from one to three groups per silicon atomselected from the group consisting of monovalenthydrocarbon radicals,aliphatic-unsaturati-on-free monovalent halohydrocarbon radicals, andcyanoalkyl radicals, there being an average per molecule of (1) of atleast two monovalent hydrocarbon radicals containing aliphaticunsaturation and the remaining valences of the silicon atoms of the saidorganosilicon polymer being satisfied by select-ion from the groupconsisting of divalent oxygen atoms, divalent hydrocarbon radicals,divalent hydrocarbon ether radicals and divalent haloarylene radicals,said divalent radicals linking silicon atoms,

(2) an organosilicon compound containing siliconbonded hydrogen atoms,there being in addition an average of up to two groups per silicon atomselected from the group consisting of monovalent hydrocarbon radicalsfree of aliphatic unsaturation, monovalent halohydrocarbon radicals freeof aliphatic unsaturation and cyan-oalkyl radicals, the remainingvalences of the silicon atoms being satisfied by groups selected fromthe group consisting of divalent oxygen atoms, divalent hydrocarbonradicals free of aliphatic unsaturation, divalent hydrocarbon etherradicals free of aliphatic unsaturation and divalent haloaryleneradicals, said divalent radicals linking silicon atoms,

there being an average at least two silicon-bonded hydrogen atoms permolecule of (2), the sum of the average number of aliphatic unsaturatedmonovalent radicals per molecule of (1) and the average ofsilicon-bonded hydrogen atoms per molecule of (2) being greater than 4,

(3) a platinum catalyst in an amount of at least 0.1 part per million Ptbased on the combined weights of (1) and (2), and

(4) sufficient benzotriazole to maintain inactivity toward curing attemperatures below 60 C.

7. A heat curable composition of matter comprising (1) a triorganosilylendblocked diorganopolysiloxane having a viscosity of at lea-st cs. at25 C. wherein the organic radicals are selected from the groupconsisting of monovalent hydrocarbon radicals,aliphatic-unsaturation-free monovalent halohydrocarbon radicals andcyanoalkyl radicals, there being an average per molecule of (1) at leasttwo monovalent hydrocarbon radicals containing aliphatic unsaturation,and in which up .to 50 percent of the silicon atoms in the said.siloxane can be connected by organic radicals selected from the groupconsisting of divalent hydrocarbon radicals, divalent hydrocarbon etherradicals, and divalent haloarylene radicals,

(2) an organosilicon compound containing siliconbonded hydrogen atoms,there being in addition an average of up to two groups per silicon atomselected from the group consisting of monovalent hydrocarbon radicalsfree of aliphatic unsaturation, monovalent halohydrocarbon radicals,free of aliphatic unsaturation and cyanoalkyl radicals, the remainingvalences of the silicon atoms being satisfied by groups seleceted fromthe group consisting of divalent oxygen atoms, divalent hydrocarbonradicals free of aliphatic unsaturation, divalent hydrocarbon etherradicals free of aliphatic unsaturation and divalent haloaryleneradicals, said divalent radicals linking silicon atoms,

there being an average at least two silicon-bonded hydrogen atoms permolecule of (2), the sum of the average molecule of 1) and the averagenumber ofsilicon-bonded number of aliphatic unsaturated monovalentradicals per hydrogen atoms per molecule of (2) being greater than 4,

(3) a platinum catalyst in an amount of at least 0.1 part per million Ptbased on the combined weights of *(1)-and (2), and

(4) sufficient benzotriazole to maintain inactivity toward curing attemperature below 60--C.

8. The composition of claim 7 wherein the organic radicals of (1) aremethyl and vinyl.

'9. The composition of claim 7 wherein the organic radicals of (1) aremethyl, phenyl and vinyl.

10. The composition of claim 7 wherein the organic radicals of (1) aremethyl, vinyl and 3,3,3-trifiuoropropyl.

11. The method which comprises (A) mixing (1) an organosilicon polymerhaving an average of from one to three groups per silicon atom selectedfrom the group consisting of monovalent hydrociarbon radical-s,aliphatic-un saturation-free monovalent halohydrocarbon radicals, andcyanoalkyl radicals, there being an average per molecule of (1) at leasttwo monovalent hydrocarbon radicals containing aliphatic unsaturation,the remaining valences of the silicon atoms of the said organosiliconpolymer being satisfied by selection from the group consisting ofdivalent oxygen atoms, divalent hydrocarbon radicals, divalenthydrocarbon ether radical and divalent haloarylene radicals, saiddivalent radicals linking silicon atoms,

(2) an organosilicon compound containing silicon bonded hydrogen atoms,there being in addition an average of up to two groups persilicon atomselected from the group: consisting of monovalent hydrocarbon radicalsfree of aliphatic unsaturation, monovalent halohydrocarbon radicals freeof aliphatic unsaturation and cyanoalkyl radi- 3,192,181 13 14 cals, theremaining valences of the silicon atoms 15. A product comprising thecured composition obbeing satisfied by groups selected from the grouptained from the method of claim 14. consisting of divalent oxygen atoms,divalent hy- 16. The method of claim 13 wherein the organicradidrocarbon radicals free of aliphatic unsaturacals of (1) are methyl,phenyl and vinyl. tion, divalent hydrocarbon ether radicals free of 17.A product comprising the cured composition obaliphatic unsaturation anddivalent haloarylene tained from the method of claim 16. radicals, saiddivalent radicals linking silicon 18. The method of claim 13 wherein theorganic radiatonis, cals of (l) are methyl, 3,3,3-trifluoropropyl andvinyl. there being an average at least two silicon-bonded 19. A productcomprising the cured composition obhydrogen atoms per molecule of (2),the sum of the 1 tained from the method of claim 18. average number ofaliphatic unsaturated monovalent 241A composition of matter comprisingradicals per molceule of (1) and the average number (1) an organosiliconcompound containing siliconof silicon-bonded hydrogen atoms per moleculeof bonded hydrogen atoms, there being in addition an (2) being greaterthan 4, average of up to two groups per silicon atom selected (3) aplatinum catalyst in an amount of at least from the group consisting ofmonovalent hydrocar- (),1 part per million Pt based on the combined bonradicals free of aliphatic unsaturation, monoweights of (l) and (2), andvalent ha'lohydrocarbon radicals free of aliphatic un- (4) suflicientbenzotriazole to reduce the activity saturation and cyanoalkyl radicals,the remaining toward curing, valences of the silicon atoms beingsatisfied by groups (B) and heating the mixture to cure the product to'a selected from the group consisting of divalent oxygen coherent solid.atoms, divalent hydrocarbon radicals free of aliphatic 12. The methodaccording to claim 11 i hi h th unsaturation, divalent hydrocarbon etherradicals free is sufficient benzotriazole to prevent curing at temperaofaliphatic unsaturation and divalent haloarylene ture below 60 C., andthe mixture is heated at a temperaradicals, Said Silicon atoms linkingSilicon atoms, ture above 60 C. to efiect cure of the product to acothere being n average of at least wo silic nonded herent solid.hydrogen atoms per molecule of (1),

13. The method which comprises (A) mixing (1) a triorganosilylendblocked diorganopolysiloxane having a viscosity of at least 100 cs.at 25 C. wherein the organic radicals are selected from the groupconsisting of monovalent hydrocarbon radicals, ailphatic unsaturationfree monovalent halohydrocarbon radicals and cy- (2) a platinumcatalyst, and

(3) at least one part by weight per part of (2) of benzotriazole.

21. The composition of claim 20, wherein (1) is amethylhydroegnsiloxane.

22. The composition of claim 20 wherein (1) is a phenylhydrogensiloxane.

23. A method of curing an organosilicon composianoalkyl radicals, therebeing an average per tion compris mixing molecule of (l) at least twomonovalent hydro- (A) an organosilicon polymer having an average ofcarbon radicals containing aliphatic unsaturafrom 1 to 3 groups persilicon atom selected from the tion, and ii111whic(li1 up to 50 percrgntof the silcgn group consisting of monovalent hydrocarbon radicals, at msint e 1 SiOXaIle Can '6 C I y aliphatic unsaturation free monovalenthalohydro- Prganic r1dia1$ Selected from the g p CPIISiSt- 40 carbonradicals, and cyanoalkyl radicals, there being mg of divalenthydroqarbon radlqals, dlvalent an average per molecule at least twomonovalent hyy l gP i Tadlcals, and dlvalent halo drocarbon radicalscontaining aliphatic unsaturation, (2 2: s gg i com 0 nd t the remainingvalences of the silicon atoms of the said g n P u corlamlng S1 FPorganosilicon polymer being satisfied by selection bonded hydrogenatoms, there being in addition 1 from tne group consisting of divalentoxygen atoms, an average of up to two groups per silicon atom div a1 6 th d b 1 1 h selected from the group consisting of monovalent th n s. ralea Iva em ydrocarbqn hydrocarbon radicals free of aliphatic unsaturaerm Y i haioarylene radicals 1 flan, monovalent halohydrocarbon radicalsfree divalent radicals linking silicon atoms with a mixof aliphaticunsaturation and cyanoa lkyl radi- 5O tulle cals, the remaining valencesof the silicon atoms (B) compnsmg being satisfied by groups selectedfrom the rou an ofganoslllcoll Compound Containing Silicont f 1 t t pbonded h d t th b dd'tconsis ing 0 Na en oxygen a oms, iva cut 3 rogen aoms, em 2; 111 a 1 1011 hydrocarbon radicals free of aliphatic unsatura-311 average of p to tWO g ps 1361 Silicon at m tion, divalenthydrocarbon ether radicals free of Selected from the group Consisting ofmOIlOVakIlt aliphatic unsaturation and divalent haloar y lenehydrocarbon radicals free of aliphatic unsatura- TZZdICaIS, saiddivalent radicals linking silicon tion, monovalent halohydrocarbonradicals free a oms, of aliphatic unsaturation and cyanoalk l raditherebeing an average at least two silicon-bonded cals, the remainingvalences of the silicoiz atoms hydrogen atoms per molecule of (2), thesum of the being satisfied by groups selected from the group averagenumber of aliphatic unsaturated monovalent consisting of divalent oxygenatoms, divalent hyradical per molecule of (1) and the average numberdrocarbon radicals free of aliphatic unsaturation, of silicon-bondedhydrogen atoms per molecule of divalent hydrocarbon ether radicals freeof ali- (2) being greater than 4, phatic unsaturation and divalenthaloarylene (3) a platinum catalyst in an amount of at least radicals,said divalent radicals linking silicon 0.1 1;1atrt gfieasnilhnzzgt basedon the combined atoms, there being an average of at least two weig s 0an an silicon-bonded hydrogen atoms per molecule (4) sutficientbenzotriazole to maintain inactivity of (1),

toward curing at temperatures below 60 C., (2) aplatinum catalyst, andand (3) at least one part by weight per part of (2) (B) heating theresulting mixture at a temperature I of benzotriazole, the amount of (2)being such above 60 C. to eifect cure to an elastomeric product. thatthere is at least 0.1 part per million of 14. The method of clairrr 13wherein the organic radiplatinum based on the combined weights (A) calsof (1) are methyl and vinyl. and (1), the amount of benzotriazole added15 16" therewith being sutficient to prevent curing of References Citedby the Examine: the combined materials at temperatures below 60 C. andthereafter heating the combined UNITED STATES PATENTS materials at atemperature of above 60 C. to 2,537 73 5 53 Wagner 2 4 5 cure themixture of a coherent solid. 5 2 43, 5 5 5 7 5 Berridge 2 4 5 24. Themethod of claim 23wherein in mixture (B) 3 020 260 2/62 Nelsgn 26Q 46 5component (1) is a methylhydrogensiloxane.

25.'The method of claim 23 wherein in mixture (B) MURRAY TILLMAN PrmmryExaminer component (1) is a phenylhydrogensiloxane. WILLIAM H. SHORT,Examiner.

11. THE METHOD WHICH COMPRISES (A) MIXING (1) AN ORGANOSILICON POLYMERHAVING AN AVERAGE OF FROM ONE TO THREE GROUPS PER SILICA ATOM SELECTEDFROM THE GROUP CONSISTING OF MONOVALENT HYMONOVALENT HALOHYDROCARBONRADICALS, AND CYANOALKYL RADICALS, THERE BEING AN AVERAGE PER ANOLKYLRADICALS, THERE BEING AN AVERAGE PER MOLECULE OF (1) AT LEAST TWOMONOVALENT HYDROCARBON RADICALS CONTAINING ALIPHATIC UNSATURATION, THEREMAINING VALENCES OF THE SILICON ATOMS OF THE SAID ORGANOSILICONPOLYMER BEING SATISFIED BY SELECTION FROM THE GROUP CONSISTING OFDIVALENT OXYGEN ATOMS, DIVALENT HYDROCARBON RADICALS DIVALENTHYDROCARBON ETHER RADICALS AND DIVALENT HALOARYLENE RADICALS, SAIDDIVALNET RADICALS LINKING SILICON ATOMS, (2) AN ORGANOSILICON COMPOUNDCONTAINING SILICONBONDED HYDROGEN ATOMS, THERE BEING IN ADDITION ANAVERAGE OF UP TO TWO GROUPS PER SILICON ATOM SELECTED FROM THE GROUPCONSISTING OF MONOVALENT HYDROCARBON RADICALS FREE OF ALIPHATICUNSATURATION, MONOVALENT HALOHYDROCARBON RADICALS FREE OF ALIPHATICUNSATURATED AND CYANOALKYL RADICALS, THE REMAINING VALENCES OF THESILICON ATOMS BEING SATISFIED BY GROUPS SELECTED FROM THE GROUPCONSISTING OF DIVALENT OXYGEN ATOMS, DIVALENT HYDROCARBON RADICAL FREEOF ALIPHATIC UNSATURATION, DIVALENTS HYDROCARBONS ETHER RADICALS FREE OFALIPHATIC UNSATURATED AND DIVALENT HALOARYLENE RADICALS, SAID DIVALENTRADICALS LINKING SILICON ATOMS, THERE BEING AN AVERAGE AT LEAST TWOSILICON-BONDED HYDROGEN ATOMS PER MOLECULE OF (2), THE SUM OF THEAVERAGE NUMBER OF ALIPHATIC UNSATURATED MONOVALENT RADICALS PERMOLECEULE OF (1) AND THE AVERAGE NUMBER OF SILICON-BONDED HYDROGEN ATOMSPER MOLECULE OF (2) BEING GREATER THAN 4, (3) A PLATINUM CATALYSTA IN ANAMOUNT OF AT LEAST 0.1 PART PER MILLION PT BASED ON THE COMBINED WEIGHTSOF (1) AND (2), AND (4) SUFFICIENT BENZOTRIAZOLE TO REDUCE THE ACTIVITYTOWARD CURING, (B) AND HEATING THE MIXTURE TO CURE THE PRODUCT TO ACOHERENT SOLID.